Neuroinflammation leads to progressive damage in ischemic stroke. Disruption of the blood-brain barrier (BBB) occurring at 24-48 h following ischemic stroke is a pathological mechanism that contributes to neuronal death. There is an urgent need to identify pharmacological strategies that limit the secondary damage following stroke. The cyclooxygenase (COX)-2/prostaglandin E2 (PGE2) pathway is actively involved in inflammatory events that exacerbate initial ischemic brain injury. Our long-term goal is to understand how the COX-2/PGE2 pathway can be manipulated to block the progressive injury cascade following ischemic stroke. The overall objective of this project is to determine how increased COX-2/PGE2 mediates BBB damage and neuronal death in ischemic stroke. Our central hypothesis is that inhibition of the COX-2/PGE2 pathway protects against BBB damage and neuronal death by reducing MMP-3/-9 production. The rationale for the proposed research is that understanding the mechanisms involved in acute (deleterious) and late (possibly beneficial) effects of COX-2/PGE2 in stroke should identify novel targets for a more selective and effective therapeutic intervention with drugs blocking the COX-2/PGE2 pathway. Specific Aim #1: To identify the downstream effectors of COX-2-mediated increase in MMP-3/-9 expression/activity and damage to the BBB after ischemia. Experiments in this aim test the hypothesis that COX-2-derived PGE2 induces MMP-3/-9 production and BBB breakdown through activation of specific EP receptor(s) in focal ischemic brain injury. We will utilize an in vivo pharmacological approach in a well- established rat model of ischemic stroke. This will be coupled with immunohistochemical, immunoblotting and biochemical analyses of EP receptors and MMP-3/-9. Specific Aim #2: To determine the therapeutic time window of protection and long-term effects of drugs modulating the COX-2/PGE2 pathway. Experiments in this aim test the hypothesis is that post- ischemic treatment with agents blocking ischemia-induced PGE2 formation/signaling provides neuroprotection without interfering in the late recovery phase. We will utilize an in vivo pharmacological approach together with innovative MRI techniques and a battery of tests to evaluate neurological function. The MRI approach will be coupled with immunohistochemical analyses to measure neurogenesis and angiogenesis. It is our expectation that this research will provide significant knowledge of the contribution of COX-2- derived PGE2 and its EP receptors to the neuroinflammatory process that follows ischemic stroke. We also expect to identify a clinically relevant therapeutic time window for the administration of drugs targeting COX- 2/PGE2. Such results would be expected to have an important positive impact, since they would identify novel and much-needed approaches to reduce the devastating consequences of stroke-induced BBB damage.